1. Field of the Invention
The present invention relates to a flash photography system including a camera body and at least one electronic flash device, wherein the amount of light of the main flash discharge is controlled in accordance with photometric readings taken from different areas of a scene at a pre-flash emission stage.
2. Description of the Related Art
Various types of conventional cameras are known in the art in which flash photography is possible and in which the amount of light of the main flash discharge is controlled in accordance with photometric readings taken from different areas of a scene at a pre-flash emission stage (preliminary flash emission) which is emitted before the main flash discharge. One of such conventional cameras is provided, as a fundamental element of a TTL (through-the-lens) photometering system thereof, with a TTL multi-segment photometering sensor (e.g., a multi-zone silicon photocell sensor) and a TTL multi-segment direct photometering sensor whose segment pattern substantially corresponds to that of the TTL multi-segment photometering sensor. In such a camera, the reflected pre-flash emission reaching the camera is received by the TTL multi-segment photometering sensor to determine the amount of light of the main flash emission in accordance with photometric readings from different zones of the TTL multi-segment photometering sensor at a pre-flash emission stage. This makes it possible to take a photograph with a flash light emission at correct exposure with respect to the subject (object).
However, in a calculation determining (calculating) the amount of light of the main flash emission becomes complicated if the TTL multi-segment direct photometering sensor is used in the above described manner. Nevertheless, in a conventional flash photography system, correct exposure cannot be attained with only a single photo-receiver (i.e., a single-segment photo-receiver) if an object having a high reflectivity such as a mirror, or the like, exists in the vicinity of the object, or if the object is relatively small with respect to the field of view.
An object of the present invention is to provide a flash photography system which makes it possible to attain correct exposure to various types of photographic subjects (objects) in flash photography without using a multi-segment flash photometering sensor of a TTL direct photometering system.
To achieve the object mentioned above, according to an aspect of the present invention, a flash photography system including a camera body and at least one flash device is provided, including a first photometering device including a multi-segment photometering sensor having a plurality of zone sensors for measuring an amount of light of a pre-flash emission, emitted by the at least one flash device before a main flash emission, respectively; a second photometering device including a single-segment direct photometering sensor for measuring an amount of light of the main flash emission emitted by the at least one flash device; a weighting device which assigns a weighting factor to an output of each of the plurality of zone sensors of the multi-segment photometering sensor; a calculation device which calculates a correction value based on each photometering value and the weighting factor of each of the plurality of zone sensors of the first photometering device, wherein an appropriate receiving light amount of the second photometering device is calculated based on the correction value; and a controller which terminates the main flash emission of the at least one flash device immediately after the light amount measured by the second photometering device reaches the appropriate receiving light amount.
Preferably, the first photometering device performs a photometering operation for each of a plurality of different photometering zones using the plurality of zone sensors. The single-segment direct photometering sensor comprises a photometering zone which includes more than one of the plurality of different photometering zones.
Preferably, the calculation device includes a first calculation which calculates a pre-flash brightness value at each of the plurality of different photometering zones, in accordance with an output of each of the plurality of zone sensors of the multi-segment photometering sensor, and calculates an average value of the pre-flash brightness values; a second calculation which calculates ratio data for each of the pre-flash brightness values, the ratio data indicating how many times the each pre-flash brightness value is greater than the calculated pre-flash brightness value; a third calculation which firstly multiplies each the ratio data by a corresponding the weighting factor, and subsequently calculates the sum thereof to obtain an estimated receiving light amount; and a fourth calculation which calculates the correction value in accordance with the estimated receiving light amount.
In the third calculation, the calculation device firstly resets the ratio data to a predetermined value if the difference between a reference pre-flash brightness value and a pre-flash brightness value for which the ratio data is calculated is out of a predetermined range, subsequently multiplies each the ratio data by a corresponding the weighting factor, and subsequently calculates the sum thereof to obtain a reference receiving light amount.
In the fourth calculation, the calculation device calculates the correction value based on the reference receiving light amount and the estimated receiving light amount which are calculated in the third calculation.
In the first calculation, the calculation device selects at least one of the pre-flash brightness values wherein the difference thereof, from a reference pre-flash brightness value, is within a predetermined range; and the calculation device calculates an average value of the selected at least one pre-flash brightness values.
Preferably, the calculation device sets the average value to the reference pre-flash brightness value in the case where none of the calculated pre-flash brightness values is within the predetermined range.
Preferably, the calculation device calculates the correction value each time the at least one flash device emits the pre-flash emission at plurality of times in succession.
Preferably, the multi-segment photometering sensor includes a TTL multi-segment photometering sensor.
Preferably, the single-segment direct photometering sensor includes a photodiode disposed at a position to receive light which is passed through a photographing lens and reflected by a film surface.
In an embodiment, the at least one flash device includes at least one slave flash unit.
According to another aspect, a camera having flash photography system including at least one flash device is provided, including a first photometering device including a multi-segment photometering sensor having a plurality of zone sensors for measuring an amount of light of a pre-flash emission, emitted by the at least one flash device before a main flash emission, respectively; a second photometering device including a single-segment direct photometering sensor for measuring an amount of light of a main flash emission emitted by the at least one flash device; a weighting device which assigns a weighting factor to an output of each of the plurality of zone sensors of the multi-segment photometering sensor; a calculation device which calculates a correction value based on each photometering value and the weighting factor of each of the plurality of zone sensors of the first photometering device, wherein an appropriate receiving light amount of the second photometering device is calculated based on the correction value; and a controller which terminates the main flash emission of the at least one flash device immediately after the light amount measured by the second photometering device reaches the appropriate receiving light amount.
Preferably, the first photometering device performs a photometering operation for each of a plurality of different photometering zones using the plurality of zone sensors. The single-segment direct photometering sensor comprises a photometering zone which includes more than one of the plurality of different photometering zones.
Preferably, the calculation device includes a first calculation which calculates a pre-flash brightness value at each of the plurality of different photometering zones, in accordance with an output of each of the plurality of zone sensors of the multi-segment photometering sensor, and calculates an average value of the pre-flash brightness values; a second calculation which calculates ratio data for each of the pre-flash brightness values, the ratio data indicating how many times the each pre-flash brightness value is greater than the calculated pre-flash brightness value; a third calculation which firstly multiplies each the ratio data by a corresponding the weighting factor, and subsequently calculates the sum thereof to obtain an estimated receiving light amount; and a fourth calculation which calculates the correction value-in accordance with the estimated receiving light amount.
In the third calculation, the calculation device firstly resets the ratio data to a predetermined value if the difference between a reference pre-flash brightness value and a pre-flash brightness value for which the ratio data is calculated is out of a predetermined range, subsequently multiplies each the ratio data by a corresponding the weighting factor, and subsequently calculates the sum thereof to obtain a reference receiving light amount.
In the fourth calculation, the calculation device calculates the correction value based on the reference receiving light amount and the estimated receiving light amount which are calculated in the third calculation.
In the first calculation, the calculation device selects at least one of the pre-flash brightness values wherein the difference thereof, from a reference pre-flash brightness value, is within a predetermined range; and the calculation device calculates an average value of the selected at least one pre-flash brightness values.
Preferably, the calculation device sets the average value to the reference pre-flash brightness value in the case where none of the calculated pre-flash brightness values is within the predetermined range.
Preferably, the calculation device calculates the correction value each time the at least one flash device emits the pre-flash emission at plurality of times in succession.
Preferably, the multi-segment photometering sensor includes a TTL multi-segment photometering sensor.
Preferably, the single-segment direct photometering sensor includes a photodiode disposed at a position to receive light which is passed through a photographing lens and reflected by a film surface.
In an embodiment, the at least one flash device includes at least one slave flash unit.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-284413 (filed on Sep. 19, 2000) and Japanese Patent Application No. 2001-34578 (filed on Feb. 9, 2001) which are expressly incorporated herein by reference in their entireties.